Oh, and all Debian/Ubuntu Xen-enabled kernels also require PAE. A Xen system was also something i wanted to try out using VirtualBox... looks like i either have to wait, compile my own xen kernel (without PAE) or try something completely different to try out xen.

A program should respect the features which the CPUID instruction delivers. As VBox guests don't see the PAE feature even on PAE CPUs they should not assume that PAE is available.

Apart from this nobody said that implementing the PAE mode is very difficult. The problem is that there are a plenty of features and bugs which are not difficult to implement or to fix respectively. We will implement this mode but we cannot promise any ETA.